This invention relates to compositions of matter useful as catalysts, to a method for preparing these catalysts, to a process wherein these compositions of matter are used as catalysts and to polymeric products produced with these catalysts. More particularly, this invention relates to catalyst compositions, to a method of making said catalyst compositions, to a method for polymerizing olefins, diolefins and/or acetylenically unsaturated monomers wherein these catalyst compositions are used, and to polymeric products produced with these catalyst compositions.
The use of soluble Ziegler-Natta type catalysts in the polymerization of olefins is, of course, well known in the prior art. In general, these soluble systems comprise a Group IV-B metal compound and a metal alkyl cocatalyst, particularly an aluminum alkyl cocatalyst. A subgenus of these catalysts is that subgenus comprising a bis(cyclopentadienyl) compound of the Group IV-B metals, particularly titanium, and an aluminum alkyl cocatalyst. While speculation remains concerning the actual structure of the active catalyst species in this subgenus of soluble Ziegler-Natta type olefin polymerization catalysts, it would appear generally accepted that the active catalyst species is an ion or a decomposition product thereof which will alkylate an olefin in the presence of a labile stabilizing anion. This theory may have first been advocated by Breslow and Newburg, and Long and Breslow, as indicated in their respective articles appearing in J. Am. Chem. Soc., 1959, Vol. 81, pp. 81-86, and J. Am. Chem. Soc., 1960, Vol. 82. pp. 1953-1957. As indicated in these articles, various studies suggested that the active catalyst species is a titanium-alkyl complex or a species derived therefrom when a titanium compound; viz., bis(cyclopentadienyl)titanium dihalide, and an aluminum alkyl are used as a catalyst or catalyst precursor. The presence of ions, all being in equilibrium, when a titanium compound is used was also suggested by Dyachkovskii, Vysokomol. Soyed., 1965, Vol. 7, pp. 114-115 and by Dyachkovskii, Shilova and Shilov, J. Polym. Sci., Part C, 1967, pp. 2333-2339. That the active catalyst species is a cation complex when a titanium compound is used, was further suggested by Eisch et al., J. Am. Chem. Soc., 1985. Vol. 107, pp. 7219-7221.
While the foregoing articles teach or suggest that the active catalyst species is an ion pair and, particularly an ion pair wherein the metal component is present as a cation or a decomposition product thereof, and while these references teach or suggest coordination chemistry to form such active catalyst species, all of the articles teach the use of a cocatalyst comprising a Lewis acid either to form or to stabilize the active ionic catalyst species. The active catalyst is, apparently, formed through a Lewis acid-Lewis base reaction of two neutral components (the metallocene and the aluminum alkyl), leading to an equilibrium between a neutral, apparently inactive, adduct and an ion pair. presumably the active catalyst. As a result of this equilibrium. there is a competition for the anion which must be present to stabilize the active cation catalyst species. This equilibrium is, of course, reversible and such reversal will deactivate the catalyst. Moreover, the catalyst systems heretofore contemplated are subject to poisoning by the presence of basic impurities in the system. Further, many if not all, of the Lewis acids heretofore contemplated for use in soluble Ziegler-Natta type catalyst systems are chain transfer agents and, as a result, prevent effective control of the product polymer molecular weight and product molecular weight distribution. Still further, most, if not all, of the cocatalysts heretofore contemplated are highly pyrophoric and. as a result, somewhat hazardous to use.
The aforementioned catalyst systems have not, generally, been particularly active when zirconium or hafnium is the Group IV-B metal used. Recently, however, it has been found that active Ziegler-Natta type catalysts can be formed when bis(cyclopentadienyl)hafnium and bis(cyclopentadienyl)zirconium compounds are used with alumoxanes. As is well known, these systems offer several distinct advantages, including vastly higher catalytic activities than the aforementioned bis (cyclopentadienyl)titanium catalysts and the production of polymers with narrower molecular weight distributions than those from conventional Ziegler-Natta catalysts. These systems remain subject to poisoning when basic impurities are present and do, however, require an undesirable excess of the alumoxane to function efficiently. Moreover, the hafnium containing systems are not as active as the zirconium containing systems, at least when used for homopolymerization. This has been suggested by Giannetti, Nicoletti, and Mazzocchi, J. Polym. Sci., Polym. Chem., 1985, Vol. 23, pp. 2117-2133, who claimed that the ethylene polymerization rates of bis(cyclopentadienyl)hafnium compounds were five to ten times slower than those of similar bis(cyclopentadienyl)zirconium compounds while there was little difference between the two catalysts in the molecular weight of the polyethylene formed from them.
In light of the several deficiencies of the coordination catalyst systems heretofore contemplated, the need for an improved coordination system which: (1) permits better control of molecular weight and molecular weight distribution; (2) is not subject to activation equilibrium; and (3) does not involve the use of an undesirable cocatalyst is believed readily apparent.